Peripheral primitive neuroectodermal tumor of the chest wall of a 69-year-old man.

We report a case of peripheral primitive neuroectodermal tumor (pPNET), which belongs to the pPNET/Ewing's sarcoma family, arising in the chest wall of a 69-year-old man. He had high levels of serum neuron-specific enolase and pro-gastrin-releasing peptide, which are believed to be useful diagnostic blood markers for small cell lung carcinoma (SCLC). Microscopically, the tumor was composed of solid nests and sheets of monotous, primitive, small round cells with a few rosettes, making it difficult to distinguish from SCLC. Immunohistochemically, the tumor cells showed intense cell membranous immunoreactivity for MIC2 protein (CD99). EWS/FLI-1 chimeric mRNA that originated from the characteristic t(11;22)(q24;q12) chromosomal translocation was detected by RT-PCR and nucleotide sequence analysis. These results confirmed the diagnostic validity of the present tumor being a pPNET, thus raising the possibility that in the past, pPNETs which have arisen in the chest have been mistakenly diagnosed as SCLC.